1. Field of the Invention
The present invention relates to a wireless base station, a network joining control method, a wireless terminal and a communication control method in a wireless network. The present invention also relates to a transmitting device, a receiving device and a wireless base station for transmitting and receiving various types of contents for which the copyright protection is necessary via a network.
2. Description of the Related Art
In recent years, in conjunction with the advance of the LAN (Local Area Network) technique, the networking in the office environment has been developed mainly in forms of wired connections among PCs (Personal Computers).
While such wired LANs are spreading, the use of the wireless LAN in which a part of the wired LAN is replaced by radio is also in progress. For example, consider the case where a wireless base station is connected to the wired LAN and a plurality of portable PCs are connected to this base station by radio. In this case, when a file of a desk-top PC connected to the wired LAN by Ethernet™ is edited from the portable PC, the radio access to the wired LAN is realized.
Also, when portions of the base station and the portable PC are extracted, these portions form a wireless LAN. The advantages of such a wireless LAN are that there is no need to lay cables because radio waves or infrared rays are used as transmission paths, and that a new construction or a layout change of the network is easy.
The introduction of such a wireless LAN is becoming popular due to the standardization of IEEE 802.11. Namely, the standardization and the research and development of the wireless LAN have been made mostly in the 2.4 GHz band and the 5 GHz band, because of the radio characteristics such as a transmission distance and a directivity, the communication policy for effectively utilizing the radio bandwidth which is a limited resource, and in view of the manufacturing cost which is preferably suppressed as low as possible from a viewpoint of the makers.
Then, in IEEE 802.11, the 2.4 GHz band wireless LAN specification was completed in 1997, and the 5 GHz band wireless LAN specification was completed in 1999. The wireless network protocols in these frequency bands basically accommodate a plurality of terminals by using the time division multiplexing.
In the 2.4 GHz band wireless LAN specification, the transmission rate is either 1 to 2 Mbps or 11 Mbps, and the specification with the transmission rate over 20 Mbps is currently under the discussion. Recently, products compatible with this 2.4 GHz band specification have been released by many companies so that the base station and the wireless PC card are now priced in an affordable range of general users.
Note that, in this 2.4 GHz band, there is a trend to install the Bluetooth™ on all kinds of devices in a variety of fields including those of portable telephones, home electronics and PCs. This Bluetooth™ is also a wireless system, and it is expected to spread worldwide due to its low cost of about $5 for one chip, its wide acceptance by approximately 2000 companies in a variety of fields, and its standardization activity that has been made in direct connection with the product developments.
On the other hand, the 5 GHz band wireless LAN specification can realize the transmission rate of 20 to 30 Mbps. Also, unlike the 2.4 GHz band, 5 GHz band is currently almost unused frequency band in which faster transmission rates can be expected easily, so that it has a high prospect of becoming the next generation wireless LAN specification, or the specification for communicating video contents such as those of TV programs and movies. It is already sold at a price of one chip at $35 in 2001, and the LSI development race is expected to become more heated up in the future.
Note that, in addition to the specification made by the IEEE in the U.S.A., there is a specification called HiperLAN2 which is made in Europe, and a specification called wireless 1394 which is made in Japan. In these three specifications, what is called physical layer (PHY layer) in the communication protocol is nearly common, but a way of defining MAC layer is different. As such, 5 GHz band is now becoming familiar.
From the circumstances described above, as wireless devices are spread, the range of application of these techniques is expected to cover not just the office environment but also the general homes as well. In particular, the fact that there is no need to lay cables in the home is possibly even greater attraction than the case of the office environment. Also, from a viewpoint that it is possible to carry out communications of the AV (Audio Visual) data, it is rather expected that their needs are higher at the homes.
In the frequency bands such as 2.4 GHz band and 5 GHz band that are intended to be used for the wireless communications, there is a possibility of being influenced by the spatial shape or other devices. In particular, in the case of the contents for which the real time characteristic is required, there is a possibility of having disturbances in the video or speech due to the occurrence of errors or the difficulty of the reproduction at constant time interval.
The 2.4 GHz band is used by the existing devices such as the microwave ovens and the portable telephones used in the U.S.A. The IEEE 802.11b wireless LAN and the ad hoc network formed by the Bluetooth devices use this frequency band, so that they have a possibility of being influenced by these existing devices. They also have a possibility of interfering with each other at a location where these two types of network coexist.
In the 5 GHz band, the standard specifications such as IEEE 802.11a wireless LAN, HiperLAN2, and ARIB wireless 1394™ are established and one of their major objectives is the faster accommodation of applications than the 2.4 GHz band. In Japan, it is limited to the indoor use, but 100 MHz band ranging from 5.15 GHz to 5.25 GHz are released to the public and four channels of 20 MHz bandwidth each can be used there. In Europe and U.S.A., other available frequency bandwidths exist.
Compared with the wired communications, the wireless communications are easier to cause bit errors at the communication path in a middle, which can degrade the video and speech if nothing is done. For this reason, the wireless communications employ the FEC (Forward Error Correction) technique in which signals are transmitted after attaching information for enabling the correction of errors at a receiving side such as the Reed-Solomon coding, or a re-transmission technique in which a receiving side is required to return an acknowledgement and signals are repeatedly re-transmitted when this acknowledgement is not received.
In the wireless communications, it is possible to determine the bit rate by a combination of the modulation scheme and the coding rate. The super fine AV data such as those of HDTV require a high bit rate. In addition, the isochronicity is required in order to communicate and reproduce the AV data in real time. For this reason, there is a need for a mechanism by which the bandwidth can be secured at interval which is as constant as possible.
Conventionally, there is a concept of the resource reservation for reserving as much of the bandwidth of the network as required by the individual application. One example of the method for reserving the bandwidth is disclosed in Japanese patent application laid open No. 2001-223716.
However, in the method in which the bandwidths declared for the purpose of the resource reservation by the individual connections are simply summed and the remaining resource is detected according to the sum, there are cases where it is difficult to stably provide the communication quality including the guarantee of the isochronicity mentioned above, because of the overhead occurring in relation to the total number of connections and the influence due to the variation of the transmission bit rate of the individual connection. It is particularly likely to encounter such cases when the resources are used near an upper limit of the bandwidth resources allowed by the network.
As described, it has been difficult to guarantee the communication quality required by each wireless terminal when a plurality of wireless terminals exist.
Also, in recent years, as the price of the wireless device in compliance with the specification of IEEE 802.11 or the like is lowering, it becomes possible to construct the wireless communication system easily and inexpensively. Also, there is a trend for the communication speed of the wireless communication system to become faster, so that a difference from a wired communication using communication cables is becomes insignificant in terms of the speed.
Recently, it is becoming possible to handle large capacity data such as AV contents easily by a computer for home use, so that it is convenient for the users if it is possible to transmit and receive data such as AV contents by using the wireless communication system.
However, if the reproduced signals of the AV contents reproduction device such as DVD player are transmitted by radio, it would be possible for all the AV contents receiving device within a prescribed range to receive them. For this reason, it is possible to consider the use of a mechanism in which only the AV contents receiving device which succeeded the authentication can receive the AV contents, so as to protect the copyright. However, there is a problem in that if the authentication at the copyright protection layer succeeds at the AV contents receiving device once, it is impossible to distinguish whether this AV contents receiving device is a formally permitted device or not.
In order to avoid such a problem, there is a proposition of the wireless communication system which realizes the secure copyright protection by preventing wireless devices other than those which are formally permitted to make accesses without a permission, in the wireless environment, as disclosed in commonly assigned co-pending U.S. patent application Ser. No. 09/934,674.
However, even when the user A sets up the access control for the device by setting an ID indicating that the user A is an owner of the device, if this ID becomes known to a user B who owns another device, the user B would be able to make access to the wireless device of the user A. For this reason, if the malicious contents owner constructs the wireless communication system and discloses the ID of the device to the public, it becomes possible to distribute the contents with the copyright protection, without a permission of the author. Consequently, this is not a fundamental solution for preventing the illegal distribution of contents, from a viewpoint of the copyright protection.